The immune system possesses the ability to control the homeostasis between the activation and inactivation of lymphocytes through various regulatory mechanisms during and after an immune response. Among these are mechanisms that specifically inhibit and/or turn off an immune response. Thus, when an antigen is presented by MHC molecules to the T-cell receptor, the T-cells become properly activated only in the presence of additional co-stimulatory signals. In the absence of these accessory signals there is no lymphocyte activation and either a state of functional inactivation termed anergy or tolerance is induced, or the T-cell is specifically deleted by apoptosis.
One such co-stimulatory signal involves interaction of CD80 on specialised antigen-presenting cells with CD28 on T-cells, and this signal has been demonstrated to be essential for full T-cell activation. (Lenschow et al. (1996) Annu. Rev. Immunol., 14, 233-258). It would therefore be desirable to provide compounds which inhibit this CD80/CD28 interaction.
Our copending international patent application PCT/GB2004/001008 relates to compounds of formula (I) and pharmaceutically or veterinarily acceptable salts, hydrates or solvates thereof:
wherein
R1 and R3 independently represent H; F; Cl; Br; —NO2; —CN; C1-C6 alkyl optionally substituted by F or Cl; or C1-C6 alkoxy optionally substituted by F;
R4 represents a carboxylic acid group (—COOH) or an ester thereof, or —C(═O)NR6R7, —NR7C(═O)R6, —NR7C(═O)OR6, —NHC(═O)NR7R6 or —NHC(═S)NR7R6 wherein                R6 represents H, or a radical of formula -(Alk)m-Q wherein                    m is 0 or 1            Alk is an optionally substituted divalent straight or branched C1-C12 alkylene, or C2-C12 alkenylene, or C2-C12 alkynylene radical or a divalent C3-C12 carbocyclic radical, any of which radicals may contain one or more —O—, —S— or —N(R8)— links wherein R8 represents H or C1-C4 alkyl, C3-C4 alkenyl, C3-C4 alkynyl, or C3-C6 cycloalkyl, and            Q represents H; —NR9R10 wherein R9 and R10 independently represents H; C1-C4 alkyl; C3-C4 alkenyl; C3-C4 alkynyl; C3-C6 cycloalkyl; an ester group; an optionally substituted carbocyclic or heterocyclic group; or R9 and R10 form a ring when taken together with the nitrogen to which they are attached, which ring is optionally substituted; and                        R7 represents H or C1-C6 alkyl; or when taken together with the atom or atoms to which they are attached R6 and R7 form an optionally substituted monocyclic heterocyclic ring having 5, 6 or 7 ring atoms; and        
X represents a bond or a divalent radical of formula —(Z)n-(Alk)- or -(Alk)-(Z)n— wherein Z represents —O—, —S— or —NH—, Alk is as defined in relation to R6 and n is 0 or 1.